1. Field of the Invention
This invention relates to a periscopic sight and more particularly to such a sight wherein long eye relief is provided without diminishing the field.
2. Description of the Prior Art
The word periscope means literally "to look around" and is applied to instruments for observing out of or into otherwise virtually inaccessible locations. Periscopes may vary from simple "over the wall" periscopes, consisting of two plain mirrors, to periscopes containing elaborate telescopic lens systems. In present day armored vehicles periscopes are furnished for the crew members for general observation and also for gun sighting. The simple mirror arrangement can be used for general viewing, but the gun sighting applications usually require a telescopic lens system with moderate magnification. The guns are mounted in turrets which are movable in azimuth relative to the vehicles. The guns are also movable in elevation within the turrets. The gun sighting periscopes are provided with an elevation scanning prism at the top to direct the images toward an objective lens and a stationary prism at the bottom to direct the objective image toward an eyepiece at an observer's station. Seals are required between the elevation prism and the objective lens as well as between the elevation prism and the surrounding environment. The objective lens, the stationary bottom prism and the eyepiece lens must also all be sealed from the surrounding environment so that moisture is prevented from fogging any of the surfaces in the lens system. Periscopic sight systems of the type described hereinabove either require that the observation point be relatively close to the eyepiece, due to short eye relief, or they require complex and expensive constructions due to the requirement for long eye relief.